Write a unit vector in the direction of the sum of the vectors

Write a unit vector in the direction of the sum of the vectors $\vec{a}=(2 \hat{i}+2 \hat{j}-5 \hat{k})$ and $\overrightarrow{\mathrm{b}}=(2 \hat{\mathrm{i}}+\hat{\mathrm{j}}-7 \hat{\mathrm{k}})$